JP2018003643A - Turbine rotor with balance weight, and balance weight - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a turbine rotor including a balance weight and provide a balance weight in which a workability in installing the balance weight to the turbine rotor can be improved, its working time can be reduced and at the same time its cost increasing can be prevented.SOLUTION: There are provided an annular groove part 12 arranged to extend in a peripheral direction around a rotating axis 10 of a turbine rotor 11 and a balance weight 14 installed inside the groove part 12. A length of the turbine rotor 11 is applied as a width. The groove part 12 includes a bottom surface 31 and an opening part 30 facing against the bottom surface 31. The opening part 30 is opened in a direction of the rotating axis 10 and a width L0 of the opening part 30 is smaller than a width L of the bottom surface 31. The balance weight 14 is provided with a first member 15 and a second member 16 that are arranged to be adjacent to each other in a radial direction of the turbine rotor 11.SELECTED DRAWING: Figure 2A

Description

  The present invention relates to a turbine rotor having a balance weight and a balance weight that can be installed on the turbine rotor.

  Gas turbines and steam turbines typically include a plurality of rotor stages, each having a row of blade rows, i.e., rotor disks that hold turbine blades. In turbines, the balance of rotating bodies such as rotors, wheels, and shafts must be adjusted to avoid damage to bearings and structural supports and excessive loads on them. This balance adjustment is performed by shaving a part of the rotating body (corrected surface) or installing a balance weight on the rotating body. The balance weight is installed at various positions of the rotating body while the position is adjusted at the assembly factory and the installation site of the turbine.

  The rotating body described in Patent Document 1 includes a groove extending in the circumferential direction on the outer peripheral surface for the installation of a balance weight. The groove portion has a bottom surface and two side surfaces that are close to each other so as to converge from the bottom surface toward the opening portion of the groove portion, and has a tapered shape in which the width of the bottom surface is larger than the width of the opening portion. The balance weight installed in such a groove has a tapered shape, is inserted into the groove from an opening (access opening) provided in the groove, is moved in the circumferential direction inside the groove, and is fixed at the installation position. .

  Patent Document 2 describes a rotating machine including a balance weight disposed in a groove having side surfaces (taper side portions) that approach each other from a bottom surface toward an opening. In the invention described in Patent Document 2, in order to place the balance weight in the groove of the rotating machine, the balance weight is inserted into the groove through the opening formed by the tapered side portion, and then moved to the installation position, and then the circumference. Rotate approximately 90 degrees in the direction and fix with the side surfaces adjacent to the tapered side of the groove.

  Patent Document 3 describes a balance weight arranged in a slot formed in a disk of a turbine rotor. This slot is formed by a disk, a flange arm and a flange. The balance weight has dimples projecting outward, and is fixed by pressing the dimples into an aperture formed in the flange.

JP2015-31368A JP 2010-261446 A JP 2010-084760 A

  In the invention described in Patent Document 1, it is necessary to insert the balance weight into the groove portion from the access opening provided in the groove portion and move the inside of the groove portion in the circumferential direction to the installation position and then fix the balance weight. In the invention described in Patent Document 2, it is necessary to insert the balance weight into the groove from the opening formed by the tapered side portion, move the inside of the groove portion to the installation position, rotate it, and then fix it. In these inventions, since the insertion position of the balance weight into the groove portion is fixed and the balance weight inserted into the groove portion needs to be moved, workability is deteriorated and the work time is increased particularly at the installation site of the turbine. There is a problem.

  In the invention described in Patent Document 3, the insertion position of the balance weight into the groove (slot) is not fixed, but it is necessary to provide a complicated structure in the turbine rotor, which increases the costs such as design cost and processing cost. There is a problem of incurring and increasing work time.

  An object of the present invention is to provide a turbine rotor having a balance weight and a balance weight, which can improve workability in installation of the balance weight to the turbine rotor, reduce work time, and prevent an increase in cost. .

  A turbine rotor provided with a balance weight according to the present invention includes an annular groove provided so as to extend in the circumferential direction around the rotation axis of the turbine rotor, and a balance weight installed inside the groove. The length in the radial direction of the turbine rotor is defined as the width. The groove includes a bottom surface and an opening facing the bottom surface, the opening opens in the direction of the rotation axis, and the width of the opening is smaller than the width of the bottom. The balance weight includes a first member and a second member disposed adjacent to each other in the radial direction of the turbine rotor.

  The turbine rotor and the balance weight provided with the balance weight according to the present invention can improve workability in the installation of the balance weight on the turbine rotor, reduce the work time, and prevent an increase in cost.

The front view of a rotor which shows the example of the installation method of the balance weight in the conventional turbine rotor. It is a sectional side view of the conventional turbine rotor in which the balance weight was installed. The front view of a rotor which shows the installation method of the balance weight in the turbine rotor by the Example of this invention. 1 is a side cross-sectional view of a turbine rotor provided with a balance weight according to an embodiment of the present invention. 1 is a side sectional view of a turbine rotor according to an embodiment of the present invention. The sectional side view of the balance weight installed in the turbine rotor by the Example of this invention. The side sectional view of the turbine rotor with which the balance weight was fixed by the example of the present invention. The front view of the turbine rotor by which the balance weight was fixed by the Example of this invention. The figure which shows the outline of a structure of a steam turbine.

  A turbine rotor according to the present invention (hereinafter also simply referred to as a “rotor”) has an annular shape provided on a surface perpendicular to the rotation axis of the rotor so as to extend circumferentially around the rotation axis and open in the rotation axis direction. A groove portion and a balance weight that is installed inside the groove portion and provides a dynamic balance of the rotor are provided. The balance weight is provided in a part of the annular groove portion in the circumferential direction.

  The groove of the rotor has a width of the opening (the length in the radial direction of the rotor) smaller than the width of the bottom surface so that the balance weight does not come off the groove. It is preferable that the groove has a tapered shape in which the width gradually decreases from the bottom surface toward the opening (that is, a shape in which the side surfaces of the groove portions approach each other from the bottom surface toward the opening). The groove portion is not formed by a complicated structure, and a conventional groove having a simple structure can be used. Therefore, it is possible to prevent an increase in cost for installing the balance weight in the rotor.

  The balance weight installed inside the groove has a portion that is larger in width than the opening of the groove so as not to be detached from the groove, and is arranged adjacent to each other in the radial direction (width direction) of the rotor. It consists of two members. Therefore, with respect to the groove portion whose width of the opening portion is smaller than the width of the bottom surface, even if there is no opening for installing the balance weight on the side surface of the groove portion, It can be easily installed inside.

  Therefore, according to the present invention, since the balance weight can be easily installed at an arbitrary position of the groove portion, the workability can be improved in the installation of the balance weight on the rotor, the work time can be reduced, and the increase in cost can be prevented. it can.

  Hereinafter, a turbine rotor having a balance weight and a balance weight according to an embodiment of the present invention will be described. In the following description, “width” is the length in the radial direction of the rotor, “width direction” is the radial direction of the rotor, and “circumferential direction” is the circumferential direction of the rotor. The turbine rotor according to the present invention may be a steam turbine rotor or a gas turbine rotor, but in the following embodiments, a steam turbine rotor will be described. Note that in the drawings shown below, the same elements are denoted by the same reference numerals, and repeated description of these elements may be omitted.

  FIG. 6 is a diagram showing an outline of the configuration of the steam turbine. The steam turbine 70 includes a casing 74, a rotor 11, a moving blade 71, and a stationary blade 72. The casing 74 stores the rotor 11, the moving blade 71, and the stationary blade 72. The rotor 11 is supported by the bearing 75 and rotates around the rotation shaft 10 by steam. The rotor blade 71 is fixed to the outer periphery of the rotor 11 via the rotor disk 73. The stationary blade 72 is fixed to the casing 74 so as to be positioned between the moving blades 71 in the direction of the rotating shaft 10.

  FIG. 1A is a front view of a rotor showing an example of a method for installing a balance weight in a conventional turbine rotor. FIG. 1B is a side sectional view of a conventional turbine rotor with a balance weight installed. In FIGS. 1A and 1B, only the upper half of the rotor is shown. In FIG. 1B, the left-right direction is the rotation axis direction of the rotor, and the up-down direction is the radial direction of the rotor.

  A typical conventional turbine rotor 51 includes an annular groove 52 provided on a surface perpendicular to the rotation shaft 50 of the rotor 51 so as to extend in the circumferential direction of the rotor 51 and open in the direction of the rotation shaft 50. In the groove 52, the width L 0 of the opening 60 (the opening facing the bottom surface 61 of the groove 52) is smaller than the width L of the bottom surface 61. An opening 53 (notch) is provided on a part of the side surface of the groove 52 in the circumferential direction.

  The balance weight 54 installed inside the groove portion 52 includes a portion (a portion facing the bottom surface 61 of the groove portion 52 in FIG. 1B) whose width is larger than the opening portion 60 of the groove portion 52. Is located in the groove 52 when the is installed in the groove 52.

  Since the balance weight 54 includes a portion having a width larger than the opening 60 of the groove 52, the balance weight 54 cannot be inserted into the groove 52 from the opening 60 of the groove 52. Therefore, an opening 53 (notch) is provided on the side surface of the groove 52, and the balance weight 54 is inserted into the groove 52 from the opening 53. The balance weight 54 is inserted into the groove 52 from the opening 53 and moved in the circumferential direction in the groove 52 to the installation position (this insertion and movement is indicated by an arrow in FIG. 1A) and fixed at the installation position. Is done.

  Thus, in the conventional turbine rotor 51, the balance weight 54 needs to be inserted into the groove portion 52 from the opening 53 on the side surface of the groove portion 52, and the inserted balance weight 54 is moved along the groove portion 52 to the installation position. Since it is necessary to move, workability | operativity deteriorates in installation of the balance weight 54, and work time may increase. Further, in the conventional turbine rotor 51, the balance weight 54 cannot be installed in the opening 53 on the side surface of the groove 52, so that the turbine rotor 51 may not be well balanced.

  FIG. 2A is a front view of a rotor illustrating a method for installing a balance weight in a turbine rotor according to an embodiment of the present invention. FIG. 2B is a cross-sectional side view of a turbine rotor with a balance weight installed according to an embodiment of the present invention. FIG. 2C is a cross-sectional side view of a turbine rotor according to an embodiment of the present invention. 2A to 2C show only the upper half of the rotor, and FIG. 2C shows a turbine rotor without a balance weight. In FIG. 2A, the direction perpendicular to the paper surface is the rotation axis direction of the rotor. 2B and 2C, the left-right direction is the rotation axis direction of the rotor, and the up-down direction is the radial direction of the rotor.

  The turbine rotor 11 according to this embodiment includes an annular groove portion 12 provided on a surface (for example, a rotor disk 73) perpendicular to the rotation shaft 10 of the rotor 11 so as to extend in the circumferential direction of the rotor 11. The groove portion 12 extends around the rotating shaft 10 and includes a bottom surface 31 and an opening 30 facing the bottom surface 31, and the opening portion 30 opens in the direction of the rotating shaft 10.

  In the groove portion 12, the width L0 of the opening 30 is smaller than the width L of the bottom surface. The groove portion 12 has side surfaces 32 and 33 on one side and the other side in the width direction. When the balance weight 14 is installed on the rotor 11, the side surfaces 32 and 33 are in contact with the side surface of the balance weight 14. As shown in FIG. 2C, an angle formed by one side surface 32 and the bottom surface 31 is α1, and an angle formed by the other side surface 33 and the bottom surface 31 is α2.

  The balance weight 14 installed inside the groove portion 12 includes a portion (a portion facing the bottom surface 31 of the groove portion 12 in FIG. 2B) whose width is larger than the opening portion 30 of the groove portion 12. Is located in the groove 12 when it is installed in the groove 12.

  The balance weight 14 includes two members disposed adjacent to each other in the radial direction of the rotor 11. One is the first member 15 and the other is the second member 16. Both the first member 15 and the second member 16 are inserted into the groove portion 12 from the opening 30 and are fixed to the installation position. The rotor 11 on which the balance weight 14 composed of the two members 15 and 16 is installed does not need to have an opening on the side surface of the groove portion 52 unlike the conventional rotor 51 (FIG. 1A), and the balance weight 14 is attached to the groove portion 12. Can be installed inside.

  In the present embodiment, the following method is used to install the balance weight 14 inside the groove 12. First, the first member 15 is inserted into the groove 12 from an arbitrary position of the opening 30. The insertion position is preferably the installation position of the balance weight 14, but may not be the installation position. When the first member 15 is inserted at a position different from the installation position of the balance weight 14, the first member 15 is moved in the circumferential direction in the groove portion 12 to the installation position of the balance weight 14. One side surface of the first member 15 is in contact with the side surface 32 of the groove portion 12. Next, the second member 16 is inserted into the groove 12 from an arbitrary position of the opening 30. The insertion position is preferably a position close to the installation position of the first member 15. Next, the second member 16 is moved inside the groove portion 12 (this movement is indicated by an arrow in FIG. 2A), and the second member 16 is disposed in the gap between the first member 15 and the side surface 33 of the groove portion 12. To do. One side surface of the second member 16 is in contact with the side surface 33 of the groove portion 12, and one side surface is in contact with the first member 15. Thereby, the installation of the balance weight 14 in the groove 12 is completed. Finally, the balance weight 14 is fixed to the groove portion 12 as will be described later.

  Note that the first member 15 and the second member 16 may be inserted into the groove portion 12 in any order.

  FIG. 3 is a side sectional view of a balance weight installed in the turbine rotor according to the embodiment of the present invention. The configuration of the balance weight 14 will be described with reference to FIG. The balance weight 14 is installed in the rotor so that the left-right direction in FIG. 3 is the rotor rotation axis direction and the up-down direction is the rotor radial direction.

  The balance weight 14 is composed of two members, a first member 15 and a second member 16. In a state where the balance weight 14 is installed on the rotor 11, the first member 15 and the second member 16 are in contact with the bottom surface 31 of the groove portion 12 and are adjacent to each other along the radial direction of the rotor 11. 15 is in contact with one side surface 32 of the groove portion 12, and the second member 16 is in contact with the other side surface 33 of the groove portion 12. That is, the balance weight 14 is divided into two members in the radial direction of the rotor 11.

  Although the 1st member 15 and the 2nd member 16 can have arbitrary shapes, it is preferable that they are the following shapes. In the state installed in the rotor 11, the width L1 of the part (bottom surface 21) which contact | connects the bottom face of the groove part 12 of the 1st member 15, and the part (bottom face 22) which contact | connects the bottom face of the groove part 12 of the 2nd member 16 Is preferably equal to the width L of the bottom surface 31 of the groove 12 (see FIG. 2B), that is, L1 + L2 = L. The sum of the width L1 of the bottom surface 21 of the first member 15 and the width L2 of the bottom surface 22 of the second member 16 is larger than the width L0 of the opening 30 of the groove portion 12, that is, L1 + L2> L0. Is preferred.

  Moreover, it is preferable that the 1st member 15 and the 2nd member 16 are the following shapes. In the state of being installed on the rotor 11, an angle θ <b> 1 formed between a portion (side surface 18) of the first member 15 in contact with one side surface 32 of the groove portion 12 (side surface 18) and the bottom surface 21 is set to the one side surface 32 and bottom surface 31 of the groove portion 12. It is preferable that the angle α1 is equal to θ1, that is, θ1 = α1. Further, in the state of being installed on the rotor 11, the angle θ <b> 2 formed by the portion (side surface 19) of the second member 16 that contacts the other side surface 33 of the groove portion 12 and the bottom surface 22 is the same as that of the other side surface 33 of the groove portion 12. It is preferable that the angle α2 formed with the bottom surface 31 is equal, that is, θ2 = α2. 2C and FIG. 3 show a case where θ1, θ2, α1, and α2 are equal to each other as an example.

  The first member 15 and the second member 16 are in contact with each other when installed on the rotor 11. The shape of the part which the 1st member 15 and the 2nd member 16 mutually contact, and the angle which contact | connect are arbitrary. For example, the inclination angle of the surface where the first member 15 and the second member 16 are in contact with each other is shown in FIG. 2B and FIG. 3 by way of example as being equal to the inclination angle θ2 of the side surface 19 of the second member 16. However, it may not be equal to the inclination angle θ2 of the side surface 19. The first member 15 and the second member 16 are preferably in contact with each other without a gap in a state where they are installed on the rotor 11.

  If the first member 15 and the second member 16 have a preferable shape as described above, the balance weight 14 (the first member 15 and the second member 16) is prevented from being detached from the groove portion 12. Thus, the vibration of the rotor 11 can be reduced, and the effect that the balance of the rotor 11 can be adjusted is further easily obtained.

  In the present embodiment, as an example, the case where the length in the width direction of the first member 15 is larger than the length in the width direction of the second member 16 is shown. The length in the width direction of the first member 15 and the second member 16 can be arbitrarily determined as long as the balance weight 14 (that is, the first member 15 and the second member 16) can be installed in the groove portion 12. . For example, the second member 16 may be longer in the width direction than the first member 15, and the first member 15 and the second member 16 may have the same length in the width direction. .

  The circumferential lengths of the first member 15 and the second member 16 can be determined by the mass of the balance weight 14. The mass of the balance weight 14 is determined so that the balance weight 14 can adjust the balance of the rotor 11. The circumferential lengths of the first member 15 and the second member 16 may be equal to or different from each other.

  In the turbine rotor 11 according to the present embodiment, the balance weight 14 can be inserted into the groove portion 12 from an arbitrary position, so that workability can be improved in installation of the balance weight 14 and work time can be reduced. Further, in the turbine rotor 11 according to the present embodiment, since it is not necessary to provide the groove portion 12 with an opening (notch) for inserting the balance weight 14 into the groove portion 12, the balance weight 14 is arranged at an arbitrary position of the groove portion 12. The turbine rotor 11 can be accurately balanced. Since a groove having a conventional structure that is not a complicated structure can be used for the groove portion 12, it is possible to prevent an increase in cost for installing the balance weight 14 in the rotor 11.

  A method of fixing the balance weight 14 (that is, the first member 15 and the second member 16) to the groove portion 12 will be described with reference to FIGS.

  FIG. 4 is a side sectional view of the turbine rotor 11 to which the balance weight 14 is fixed according to the embodiment of the present invention, and corresponds to FIG. 2B. In FIG. 4, the left-right direction is the direction of the rotation axis of the rotor, and the up-down direction is the radial direction of the rotor. FIG. 4 shows an example in which the balance weight 14 is fixed using the screwing member 17. The first member 15 includes an internal thread portion 23 (a hole having a thread on the inside) that extends in the direction of the rotating shaft 10 of the rotor 11, and a screwing member 17 is inserted into the internal thread portion 23. When the screwing member 17 is rotated and inserted into the female screw portion 23, the side surface 18 of the first member 15 and the side surface 19 of the second member 16 are pressed against the side surface 32 and the side surface 33 of the groove portion 12, respectively, and the balance weight. 14 is fixed.

  For example, a screw or a bolt can be used as the screwing member 17. However, it is preferable to use a screw having no head called a ginger screw because the screwing member 17 does not protrude outside the groove portion 12.

  FIG. 4 shows an example in which the first member 15 includes the female screw portion 23. However, the female screw portion 23 is provided on at least one of the first member 15 and the second member 16, and the female screw portion 23 is threaded. 17 may be inserted. When the screwing member 17 is inserted into one of the first member 15 and the second member 16, the length in the width direction of the member into which the screwing member 17 is inserted is the length in the other width direction. It is preferable to make it larger than this.

  FIG. 5 is a front view of the turbine rotor 11 to which the balance weight 14 is fixed according to the embodiment of the present invention, and corresponds to FIG. 2A. FIG. 5 shows only a part of the rotor 11 (the balance weight 14 and its vicinity), the direction perpendicular to the paper surface is the direction of the rotating shaft 10 of the rotor 11, and the vertical direction is the radial direction of the rotor 11. . FIG. 5 shows an example in which the balance weight 14 is fixed by providing the convex portions 20 on the side surface 32 and the side surface 33 of the groove portion 12. Two convex portions 20 are provided on the side surface 32 of the groove portion 12 so as to be in contact with both ends in the circumferential direction of the side surface 18 of the first member 15, and the side surface 19 of the second member 16 is provided on the side surface 33 of the groove portion 12. Two convex portions 20 are provided so as to be in contact with both ends in the circumferential direction. The balance weight 14 is fixed to the rotor 11 by the four convex portions 20 without moving in the circumferential direction. The convex portion 20 can be formed, for example, by plastically deforming the side surfaces 32 and 33 of the groove portion 12 using a hammer and a punch.

  In addition, this invention is not limited to said Example, A various deformation | transformation is possible. For example, the above-described embodiments are described in detail for easy understanding of the present invention, and the present invention is not necessarily limited to an aspect including all the configurations described. In addition, a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment. It is also possible to add the configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to delete a part of the configuration of each embodiment or to add or replace another configuration.

  DESCRIPTION OF SYMBOLS 10 ... Rotary shaft, 11 ... Turbine rotor, 12 ... Groove part, 14 ... Balance weight, 15 ... 1st member of balance weight, 16 ... 2nd member of balance weight, 17 ... Screwing member, 18 ... 1st Side surface of member, 19... Side surface of second member, 20... Convex portion, 21 .. bottom surface of first member, 22 .. bottom surface of second member, 23. The bottom of the groove, 32, 33 ... the side of the groove, 50 ... the rotating shaft, 51 ... the turbine rotor, 52 ... the groove, 53 ... the opening on the side of the groove, 54 ... the balance weight, 60 ... the opening on the groove, 61 ... 70: steam turbine, 71: moving blade, 72: stationary blade, 73: rotor disk, 74: casing, 75: bearing, L0: width of the opening of the groove, L: width of the bottom of the groove, L1 ... the width of the bottom surface of the first member, L2 ... the second member The width of the bottom surface, α1... The angle formed between one side surface and the bottom surface of the groove portion, α2... The angle formed between the other side surface and the bottom surface of the groove portion, θ1. The angle formed by θ2: the angle formed by the side surface and the bottom surface of the second member that are in contact with the side surface of the groove.

Claims (10)

An annular groove provided to extend in the circumferential direction around the rotation axis of the turbine rotor;
A balance weight installed inside the groove,
When the length in the radial direction of the turbine rotor is a width,
The groove includes a bottom surface and an opening facing the bottom surface, the opening opens in the direction of the rotation axis, and the width of the opening is smaller than the width of the bottom surface,
The balance weight includes a first member and a second member arranged adjacent to each other in the radial direction of the turbine rotor.
A turbine rotor having a balance weight. In the balance weight, the side surface of the first member is in contact with one side surface of the groove portion, the side surface of the second member is in contact with the other side surface of the groove portion, and the bottom surface of the first member and the second surface The bottom surface of the member is in contact with the bottom surface of the groove,
An angle formed between the side surface of the first member and the bottom surface of the first member is equal to an angle formed between the one side surface of the groove and the bottom surface of the groove.
An angle formed between the side surface of the second member and the bottom surface of the second member is equal to an angle formed between the other side surface of the groove and the bottom surface of the groove.
The turbine rotor provided with the balance weight of Claim 1. In the balance weight, the bottom surface of the first member and the bottom surface of the second member are in contact with the bottom surface of the groove,
The sum of the width of the bottom surface of the first member and the width of the bottom surface of the second member is equal to the width of the bottom surface of the groove portion,
The turbine rotor provided with the balance weight of Claim 1. In the balance weight, the bottom surface of the first member and the bottom surface of the second member are in contact with the bottom surface of the groove,
The sum of the width of the bottom surface of the first member and the width of the bottom surface of the second member is larger than the width of the opening of the groove portion,
The turbine rotor provided with the balance weight of Claim 1. The balance weight includes an internal thread portion in which at least one of the first member and the second member extends in the direction of the rotation shaft,
A screwing member is inserted into the female screw part,
The turbine rotor provided with the balance weight of Claim 1. In the balance weight, the first member is in contact with one side surface of the groove portion, the second member is in contact with the other side surface of the groove portion,
The one side surface of the groove portion includes two convex portions in contact with both end portions in the circumferential direction of the first member,
The other side surface of the groove includes two convex portions that are in contact with both ends of the second member in the circumferential direction.
The turbine rotor provided with the balance weight of Claim 1. It is an annular groove provided with a bottom surface and an opening facing the bottom surface, and is provided so as to extend in the circumferential direction around the rotation axis of the turbine rotor, and when the length in the radial direction of the turbine rotor is a width, The opening is opened in the direction of the rotation axis, and the width of the opening is set inside the groove that is smaller than the width of the bottom surface;
A first member and a second member disposed adjacent to each other in the radial direction of the turbine rotor;
Balance weight characterized by that. The side surface of the first member is in contact with one side surface of the groove,
The side surface of the second member is in contact with the other side surface of the groove,
The bottom surface of the first member and the bottom surface of the second member are in contact with the bottom surface of the groove,
An angle formed between the side surface of the first member and the bottom surface of the first member is equal to an angle formed between the one side surface of the groove and the bottom surface of the groove.
An angle formed between the side surface of the second member and the bottom surface of the second member is equal to an angle formed between the other side surface of the groove and the bottom surface of the groove.
The balance weight according to claim 7. The bottom surface of the first member and the bottom surface of the second member are in contact with the bottom surface of the groove,
The sum of the width of the bottom surface of the first member and the width of the bottom surface of the second member is equal to the width of the bottom surface of the groove portion,
The balance weight according to claim 7. The bottom surface of the first member and the bottom surface of the second member are in contact with the bottom surface of the groove,
The sum of the width of the bottom surface of the first member and the width of the bottom surface of the second member is larger than the width of the opening of the groove portion,
The balance weight according to claim 7.

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